Surface micromachining has become a popular method for fabricating micromechanical sensors and actuators. In the most commonly used method of forming micromechanical devices, polysilicon is used as the mechanical material. The process involves starting with a substrate. A layer of sacrificial material is deposited on the substrate. A via or other void is provided in the sacrificial layer. The mechanical material, typically polysilicon, is deposited and patterned to form the micromechanical structure. The sacrificial layer is then removed, leaving the micromechanical structure attached to the substrate and having a portion suspended over the substrate. All the structures formed in this manner tend to be generally parallel with the substrate. The distance the suspended part of the structure is disposed above the substrate is typically 2 microns, which limits the degree of movement of the suspended microstructure before it contacts the substrate.
A drawback associated with typical micromechanical devices is that suspended structures are limited to a gap of only a few microns between the suspended portion of the structure and the substrate. As such, the movement of the suspended structure relative to the substrate is severely limited.
Referring now to FIG. 1, a typical micromechanical device formation process is shown. Initially, a layer of sacrificial material 20 is deposited on a substrate 10. At the next step a via 30 is produced in the sacrificial layer. At the next step a layer of material, typically polysilicon, is deposited, forming the micromechanical structure 40. At the next step the micromechanical structure 40 is released by removal of the sacrificial layer 20. As can be seen, the micromechanical structure 40 is only movable a small distance (typically 2 microns) before it contacts the substrate.
A technique has been developed which attempts to overcome the problem of limited movement of the suspended micromechanical structure by utilizing hinges which rotate the structure further away from the substrate after the micromechanical structure is formed. Additionally, mechanical latching has been used to support the micromechanical structures once formed. These devices have proven to be very difficult to manufacture, especially in large quantities. It would be desirable to be able to manufacture a micromechanical structure having a more pronounced three dimensional aspect and a concomitant larger degree of movement with respect to the substrate.